Water-resistant glue and method of making the same



Patented June 17, 1941 WATER-RESISTANT GLUE AND METHOD OF MAKING THE SAME John 1;. Hubbard, Gowanda, N. Y., assignor to Peter Cooper Corporation, Gowanda, N. Y.

No Drawing.

Application April 24, 1939, Serial No. 269,789

Claims. (01. 134-231;)

This invention relates to improvements in glue, and particularly to water-resistant glue and methods of making the same.

It is well known that glue can be rendered water-resistant by reacting on the glue with certain materials having a,tanning action on the protein substances of theglue. Due to the fact that such tanning materials will coagulate glue solutions of average-concentration when added directly to such solutions, these materials are either added to the diluted glue size, as in tub sizing of paper, or are applied to the glue after the same has been spread upon a surface. This latter method, is quite practical in connection with the waterproofing of glue when used as a size for specialty type paper or other materials or when used in connection with a coating preparation, as for example in the manufacture of wall paper. It has heretofore been found impractical to add such tanning materials to glue solutions of average concentration such. as are desired, for example, if the glue solution is used as an adhesive for gluing wood or the like, or for a stock glue solution to be added towall paper colors, sizinQ'solutions, or the like, for the reason that if such tanning materials are added to a glue solution of average concentration, containing for example from 25% to 40% of glue, in sufficient quantities to effectively coagulate the glue to render it satisfactorily water-resistant, then a coagulating or thickening action occurs which destroys the flowing properties of the glue and/or destroys the ability of the glue to attach itself firmly toa surface, and thus makes 'it impossible to produce the desired adhesive effects.

One of the objects of this invention'is to provide a glue solution containing a relatively large proportion of glue, which, when applied. to a surface and allowed to set, forms a water resist- Another object is to provide aglue ant glue. solution having a waterproofing or tanning agent incorporated therein prior to the application of the glue to a surface, and in which means are provided for preventing or retarding the reaction of the water-proofing agents with the glue until after the glue has begun toset or harden.

A further object is to provide a glue solution of this kind which contains a waterproofing ingredient and which solution has been rendered. somewhat acid by the addition of a weak volatile acid, to prevent coagulation of the glue until after the same has been applied to a surface.

A further object of this invention is to provide a method of preparing a glue solution in such a manner that the glue, when set or hardened, will I prefer to employ as tanning or hardening agents commercial aluminum and chromium salts, which without change have a tanning acglue solutions to coact with all or the greater part of the reactive protein material of the glue solutions. The amount of these salts that must be added to glue solutions depends upon the grade of glue used, smaller quantities being required for higher grade glues than forlower grades.

The most satisfactory tanning or coagulation of glue by means of these salts takes place when the glue is at or near its iso-electric point,which is at a pH of about 4.7 to 4.9. At a pH of 4.6

to 4.4, or below, the tannage is markedly inferior or non-existent depending on specific conditions of concentration of theglue, grade of glue and weight of tanning materials. At a pH of 4.7 to 5.2, particularly if borax has been added, the tannage and coagulation of the glue is extremely satisfactory. At pH values above 5.2, the tannage of the glue becomes increasingly inferior although the glue may still coagulate or thicken under specific conditions as to concentration of glue, grade and weight -of tanning agent.

In concentrated glue solutions of this kind containing a tanning agent of this type with the pH of said solution adjusted in the range of pH 4.7 to 5.2, the glue tends to coagulate and under these conditions glue solutions containing less glue tend to thicken appreciably. Furthermore, in most cases, if the required amount of tanning or hardening agent for optimum tannage results is added to a glue solution, the pH of the solution becomes less than that of an iso-electric solution; If it is attempted to remedy this condition by merely adding sufficient alkali to the glue' solution to bring the pH of the solution up to the :iso-electric point or slightly above, then the solution becomes coagulated or thickened and is impractical for use.

In accordance with my invention, I overcome these difficulties by providing a glue solution which contains suflicient of these tanning salts to produce the full or satisfactory tanning or hardening action on the glue, by" providing in "the glue solution sufficient alkali, preferably in the form of borax to bring the pH of the solution to approximately the iso-electric point, and I also provide an acid which is volatile and which keeps the pH of the solution down to a point at which the solution will not coagulate, this acid volatili'zing upon setting and drying of the glue so that the remaining glue film attains the pH at near the iso-electric point, at which the most eifective tanning action takes place.

In order to produce a glue of this kind, the ingredients may be mixed in any desired manner, taking care, however, that the solution containing glue and tanning agent is not allowed to reach a pH above about 4.0 to 4.5, since above this point, coagulation and/or thickening is pronounced. By way of example, I may produce my improved water-resistant glue by adding to water at a temperature from about 140 F. to about 180 R, an aluminum or chromium salt of the type which per se has a tanning action on the glue, or in other words, salts in which the chromium or aluminum is present in the basic radical, and borax in such quantities as may be required by the type and quantity of salt used. When these salt-s have been dissolved, I add to the solution, the re-' quired quantity of a volatile acid, such as acetic acid or formic acid. The acid will dissolve the curdy precipitate of boric acid and/or basic metal hydroxide. The required amount of dry glue is then added, and the mass is stirred until a smooth composition has been obtained.

Any other manner of mixing the ingredients may be employed, but it must be borne in mind that it is essential that the acid be added to the glue solution either simultaneously with the tanni'ng salt or before the tanning salt is added,-

is smooth. The addition of the glue will lower the temperature of the composition to about 130 to 140 F., anddue to the volatility of the formic acid, it is advisable to keep the temperature of the solution below 140 F. during solution and storage of the composition.

The resulting composition will have a pH of about 3.6 to 3.8 possessing excellent working properties with freedom from coagulation. When this composition is spread as a film, it has the advantage or setting very rapidly, so that it is well adapted for use in machines, as well as by hand. During the drying of the film, the volatile formic acid evaporates and to some extent may be absorbed by the material to which the glue has been applied, thus raising the pH of the resulting film to about 4.7 to 5.2, so that during the passing off of the volatile acid, the pH of the glue film passes .through the iso-electrio point.

By having the pH of thefilm pass through and slightly above the iso-electric point of glue (generally accepted as pH 4.7), the practical results so obtained are somewhat superior to those obtained by controlling the pH just at the isoelectric point of pH 4.7. While a pH of 4.7 gives good tannage, by driving the pH through the isoelectric point to a pH of 4.9 to 5.2 excellent tannages are obtained which are more permanent, particularly if borax has been added to the composition.

It has previously been stated that the grade of glue. is one of the variables governing the coagulating effect 01. aluminum salts on glue solutions of a given system. The grade of a glue is indirectly a measurement of the relative percentage of free, true protein present as differextent to require the addition of any alkali, such as borax, and in such case, the alkali may be entirely omitted, or only a small amount used.

Any of the usual grades of glue may be employed in connection with my invention, but the quantities of other ingredients used must be such as required for the particular glue employed. Any of the commercially available salts of aluminum or chromium may be employed which per se act as tanning agents. Alkalies other than borax may be used to neutralize the acidity of the glue solution, but for reasons hereinafter stated, borax is preferred, since its use results in an increased water-resistance of the resulting glue film. Any weak or organic volatile acid may be used, acetic acid, formic acid or proplonic acid being preferred, since they are most readily available and do not attack the glue.

The following examples are given by way of illustrating some embodiments of my invention, it being understood, however, that it is not intended to limit this invention for'use only with the specific examples given.

A typical formula for general use includes 30 pounds of glue, 80 pounds of water, 5 pounds of aluminum sulfate, 6 .pounds of borax, and 6v pounds of 90% formic acid. The water, aluml num sulfate and borax, are placed in a jacketed pan or kettle and heated to about 160 F. When the salts are dissolved in the water, the formic acid is added to dissolve the curdy precipitate of the boric acid and/or basic aluminum hydroxide and the glue is then quickly added, Preferably, the glue is ground to a fineness of about 30 mesh, so as to dissolve quickly in the solution, which is stirred until the resulting composition ing from the proteo'se and peptone hydrolysis products found with the true protein in all commerclal glues. The true protein is strongly coagulated by a given weight of aluminum salt whereas the proteose and peptone hydrolysis products require a considerable higher concentration of the same' aluminum salt to promote coagulation. Thus the higher the grade of the glue. the higher the percentage 01 strongly coagu ated protein, and the less the concentration of aluminum salt required to bring about satisfactory waterproofing qualities.

Experiments have shown that the following table ives satisfactory Waterproof adhesives us ing high, medium and low grades of glue:

In examples herein given, high grade glue referred to is Peter Cooper Standard A Extra, the

medium grade glue is Peter Cooper Standard I XM, and the low grade glue is Peter Cooper Standard DB #2.

The above ratios of aluminum sulfate to dry glue will insure good water-resistant dried glue films. If smaller Weights of aluminum sulfate are used, the resultant waterproofing effect is diminished.

Experiments have shown that other aluminum salts may be used as a source of trivalent aluminum ions for waterproofing effect upon glue protein. Aluminum chloride and aluminum nitrate have both proven satisfactory. With these salts, such weights were used in the general formula as to give equivalent weights of aluminum trivalent ions in the adhesive equal to the weight of trivalent aluminum ions present in the formulas using aluminum sulfate. The following formulas representing concentrated adhesives suitable for sizing clay slips for application on paper gave equivalent pH values for the dried films with The above salts are commercially available and are relatively clieap, serving as convenient sources of alumium ions, but any other aluminum salts can be used, provided that trivalent aluminum ions are present in dissociated form to react with the glue protein. Such salts per se have a tanning or hardening action on the glue and do not require any chemical change in order to render them active as tanning or hardening agents. In these sales the aluminum i present in the basic radical.

The potassium. ammonium and sodium alums may also be used. taking into consideration the aluminum ion content concentration and correcting the adhesive with borax or other alkali for the desired pH of the dried adhesive film.

Experiments have shown that acetic. acid may be used in place of formic acid in all formulas, but due to the lower dissociation of the acetic acid as compared with formic, it requires about three times as much acetic acid as formic acid (90% formic and glacial acetic acids).

Because of the fact that there are available many grades of glue, definite rules cannot be given for making my improved water-resistant adhesive. In carrying out my invention, however, the following general rules should be observed, when producing the same.

For good waterproofing effect, the quantity of aluminum sulfate, or equivalent weight of other aluminum salt should be about of the weight of the high grade glue, 16% of the weight of a medium grade glue and about 30% of the weight of a low grade glue. After determining the waterglue concentration desired, it is advisabl to find out by experiment the minimum concentration of formic or acetic acid required to prevent coagulation and assure a smooth flowing adhesive. It

should then be determined by experiment how much borax or other alkaline agentisrequired to give a dry film of a pH 4.7 to 5.2. The acid content should then be corrected to compensate for the addition of the alkaline agent.

When chromium salts are used to produce the water-resistant adhesive, very excellent waterresistant properties are obtained, but the glue solutions thus formed have a working life which is somewhat less than that of water-resistant glues made with aluminum salts, due to a progressive irreversible tannage in the glue'solutions made with chromium salts, which is intensified by heat. If exposed to moderate room temperatures, these chromium salt glue solutions may, however, be

kept for three or four days before the tannage proceeds to an excessive extent. The usual chrome salts of commerce are not as acid as the corresponding aluminum salts, and for this reason, borax or other alkaline materials in most cases are not needed for correct-ion of the pH of the dried adhesive film.

Examples as to how water-resistant compositions may be made with chromium salts with three grades of glue are as follows:

Grams High grade glue 30 Water 80 Formic acid 6 1 Chrome alum -s 2 Medium grade glue 30 Water 80 Formicacid 6-7 Chrome alum 3 Low-grade glue 30 Water 80 Formic acid 64 Chrome alum 5 Equivalent weights of other chrome salts may be used in place of the chrome alum as outlined above.

It is, of course, also possible to produce excellent water-resistant glue films by using mixtures of chromium and aluminum salts and under such conditions, it is very desirable to add some borax or other alkali for the purpose of obtaining the desired pH value of the dried film. Any of the well known and commercially available chromium salts may be used, which per se have a tanning action on glue and in which the metal is present in the basic radical, including either of the two chrome alums, namely, chromic potassium sulfate and chromic ammonium sulfate, as

well as chromic chloride, nitrate, sulfate, and hydroxide. the latter being dissolved in an appropriate acid. In substituting these other chromium salts, it is merely necessary to use them in quantities such that equivalent weights of tri-" valent chromium ions will be present inthe solution, as are present in the chrome alum employed in the foregoing formulas.

In connection with these formulas. the ingredients may be brought together in any suitable manner. For example, very satisfactory results can be obtained by adding 50 parts of water to a jacketed kettle, then adding theformic acid, and then the dry glue, preferably in finely 'divided form, so that it will quickly-"go into solution at a temperatur of about F. In a separate container. the chromium salt is dissolved in the remaining 30 parts of water, heat being used if desired. This chrome alum solution at a temperature generally not in excess of 130 F. is

water-resistant.

aluminum sulfate.

added to the warm glue solution while the same is being stirred.

In preparing my improved water-resistant glue solutions, the nature of the surface to which the adhesive is to be applied must also be taken into consideration. These surfaces may be acid or alkaline, and if so, the pH of the glue solution must be adjusted so that the final glue film will have the desired pH of about 4.7 to 5.2.

The glue solutions herein described may be used for ordinary adhesive purposes in place of other glue or adhesive solutions, and the glue films thus formed will have the advantage of being highly Furthermore, the glue is fast setting, which makes it very desirable for operations in which the gluing is done by machines.

In addition to the use of these glue solutions as adhesives, the solutions herein described may be used as stock solutions for addition to pulp colors or clay slips used in the coating of wall papers,

-fabrics, and the like. In my Patent No. 2,043,324.

I have described a composition and process for producing water-fast wall papers, and the like, in which the web after the printing i treated with a water proofing composition. When water-resistant glue solutions as herein described are used, the waterproofing ingredients are incorporated in the colors used in printing the wall paper or fabric so that water-resistant web are produced without requiring the additional operation of treatment with the waterproofing materials as described in the beforementioned patent. The composition herein described, therefore, saves one operation in the manufacture of water-fast wall papers and similar fabrics. Since chromium salts as a rule are colored, it is, of course, preferred to use the aluminum salts in connection with pulp colors or clay slips for coating webs. Similarly, my improved water-fast glue solutions may be added to sizing solutions to produce water-resistant papers or fabrics.

It will, of course, be obvious that, if it is desired to make a still more quickly drying glue so lution, a part of the water of my improved glue solution may be replaced by alcohol. Also if it is desired to form a liquid glue, which will remain in liquid form for long periods of time, acetic acid may be used in place of a part or all of the water. Also for plasticizing effect, any suitable plasticlzing materials compatible with the composition may be used, provided such plasticizers do not retard or prevent the glue tannage. Glycerine, for example, is suitable for use with the compositions containing aluminum salts.

While any alkali may be used to raise the pH of the glue film, I have obtained the best results by the use of borax. It was observed on prolonged water treatment that the borax treated adhesive composition films were much more stable and waterproof than where sodium acetate or caustic soda was used for correction of the pH of the dried films. This was found to be due to the formation of boric acid within the concentrated adhesive by reaction of the borax with the hydrogen ions of the dissociated sulfuric acid from the On drying of the adhesive film, the boric acid due to its low solubility and low dissociation withdraws hydrogen ions from solution tending to lower the active acid content of the adhesive and raise the pH of the film through the iso-electric point of the glue while the volatile formic or acetic acid is driven off by the stronger dissociated non-volatile sulfuric acid present. On wetting the dried film with tap water the boric acid does not dissociate to any great extent being weakly dissociated and also is relatively slightly soluble. The boric acid thus acts as a buffer in holding back hydrogen ions which, if actively dissociated, would tend to promote softening of the film. Boric acid also has a pH of about 5.2 tending to a limited extent to serve as a true buffer salt. The small amount of free acid present in the adhesive film is insumcient to promote rapid swelling or hydration of the glue film, and such acid is quickly neutralized by the alkalinity present in the tap water. The boric acid in the film tends to buffer the film against excess alkalinity in the water, tending to hold the pH of the film near a pH of 5.0 for some little time. The adhesive film is exceptionally waterproof not only because of the above helpful features but due to the fact that as the film be comes increasingly alkaline through tap water treatment the glue film becomes increasingly negatively charged, reacting with the positively charged aluminum ions causing a raising of the melting point and a hardening effect upon the glue protein.

I claim as my invention:

1. A composition for producing a water-resistant glue film, said composition including a glue solution, a tanning agent comprising a salt of a metal selected from a group consisting of aluminum and chromium wherein said metal is present in the basic radical and which salt per se has a tanning action on glue, said composition including at least 6 /2% of said tanning agent based upon the quantity of glue in said composition, an alkali, and a volatile organic acid which reduces the pH of said composition to less than about 4.5, the quantity of alkali being such that the glue film after volatilization of said acid will have a pH from about 4.7 to 5.2.

2. A composition for producing a water-resistant glue film, said composition including a glue solution containing from about 25% to 40% of glue, a tanning agent comprising a salt of a metal selected from a group consisting of aluminum and chromium wherein said metal is present in the basic radical and which salt per se has a direct tanning action on the glue, said composition including from ti /2% to 16% of said tanning agent, based upon the quantity of glue in said composition, and a volatile organic acid which reduces the pH of said composition to less than 4.5, said solution being adjusted so that the same without said volatile acid has a pH of about 4.7 to 5.2.

3. A composition for producing a water-resistant glue film, said composition including a solution containing glue, an aluminum salt in sufficient quantity to effectsubstantially complete tanning of the glue, a volatile organic acid which reduces the pH of the composition to a point at which tanning is retarded, and an alkali in sufficient quantity so that said solution without said acid would have a pH of about 4.7 to 5.2.

4. A composition for producing a water-resistant glue film, said composition including a solution containing glue, a salt of a metal selected from a group consisting of aluminum and chromlum wherein said metal is present in the basic radical and which salt per se has a tanning action on glue, in sufficient quantity to effect substantially complete tanning of said glue, borax, and an acid selected from a group including acetic acid and formic acid, in sufficient quantity to reduce the pH of the composition to a point at which tanning is retarded, the quantity of borax in said composition being sufllcient so that the composition without said acid would have a pH of from about 4.7 to 5.2.

5. A composition for producing a water-resistant glue film, said composition including a glue solution containing from about 25% to 40% of glue, a tanning agent comprising a salt of a metal selected from a group consisting of aluminum and chromium wherein said metal is present in the basic radical and which salt per so has a direct tanning action on the glue, thequantity of said tanning agent being from 6 to 16% by weight of the quantity of the glue in said solution, borax, and formic acid in a quantity suflicient to reduce the pH of the composition to less than 4, the quantity of borax being such that the composition without said acid would have a pH of about from 4.7 to 5.2.

6. In a process of producing a glue solution for producing a water-resistant glue the steps of making a glue solution including a volatile organic acid selected from a group consisting of formic acid and acetic acid, a tanning salt of a metal selected from a group consisting of aluminum and chromium and which salt per se has a direct tanning action on the glue, the quantity of said tanning agent being from 6 /2% to 16% by weight of the quantity of the glue in said solution, said acid beingadded in quantities suiiicient to reduce the pH of said solution to that at which the tanning of the glue is retarded, and adjusting said solution by addition thereto of such quantity of alkali as is necessary to produce a glue which after volatilization of said acid has a pH of about 4.7 to 5.2.

7. A process of producing a water-resistant glue film, which includes making a glue solution containing a volatile organic acid selected from a group consisting of acetic acid and formic acid, and a tanning agent comprising a salt of a metal. selected from a group consisting or aluminum and chromium wherein said metal is present in tion to a surface to form a film,

the basic radical and which salt per se has a direct tanning action on the glue, adjusting said solution by the addition of sumcient alkali to produce a solution which without said acid would have a pH of about 4.7 to 5.2, applying said soluand evaporating said volatile acid from said fllm to raise the pH of said fllm to a point at which active tanning of said glue takes place.

8. A process of producing a water-resistant glue film, which includes making a glue solution containing a volatile organic acid selected from a group consisting of acetic acid and formic acid, and a tanning agent comprising a salt of a metal selected from a group consisting of aluminum and chromium wherein said metal is present in the basic radical and which salt per se has a direct tanning action on the glue, the quantity of said tanning agent being from 6 /2% to 16% by weight of the quantity of the glue in said solution, adjusting said solution by the addition thereto of borax in suflicient quantity to produce a solution which without said acid would have a pH of about 4.7 to 5.2, applying said solution to a surface to form a film, and removing said acid from said film by volatilization.

9. A process of producing a water-resistant glue film, which includes making a glue solution containing a volatil organic acid selected from a. group consisting of acetic acid and formic acid, and suflicient trivalent aluminum salt to completely tan the 'glue in said solution, said acid being present in sufficient quantity to retard the tanning action of said salt on said glue, and an alkali in sufllcient quantity so that the pH of said solution without said acid would be from about 4.7 to 5.2, applying said solution to a surface to form a film, and volatilizing said acid.

10. A process in accordance with claim 6 characterizedin that borax is used as the alkali.

JOHN R. HUBBARD.

. CERTIFICATE OF CORRECTION. Patent No. 2, 2I+6,lio5. June 17, 19in.

' JOHN R. HUBBARD.

It is hereby certified that the name of the assignee in the above numbered patent was erroneously written and printed as "Peter Cooper Corporation" whereas said name should have been written and printed it -Peter Cooper Corpprations, of Gowanda, New York-, as shown by the record of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of July, A. D. 191 1.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

